Pump



mus-v March 15, 1960 G.IR. FINDLAY PUMP Filed Sept. 16. 1953 3 Sheets-Sheet l ATTORNEY March 15, 1960 FINDLAY 7 2,928,349

PUMP

Filed Sept. 16, 1953 3 Sheets-Sheet 2 Pole piece l-1 ceni'er line Weak s'l'ruy field FIG. 2

IN V EN TOR.

v 0M4, R. m1,

ATTORNEY March 15, 1960 G. R. FINDLAY PUMP Filed Sept. 16, 1953 FIG. 4

3 Sheets-Sheet 3 ATTORNEY Unit PUMP

Application September 16, 1953, Serial No. 380,550

2 Claims. (Cl. 103-1) This invention relates to magnetic pumps and more particularly to a magnetic drag pump for handling electro-conducting fluids such as liquid metals.

A principal object of the present invention is to provide an improved pump of the above type embodying novel features of design by which high power efficiency and improved pumping action are obtained.

Other objects of the invention will in and will in part appear hereinafter.

The invention accordingly comprises the apparatus possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings wherein:

Fig. 1 is a diagrammatic, schematic, fragmentary, partially sectional view of one preferred embodiment of the invention;

Fig. 2 is an enlarged fragmentary View of a portion of Fig. 1;

Fig. 3 is an enlarged sectional view taken along the line 33 of Fig. 1;

Fig. 4 is an enlarged sectional view of an alternative embodiment of the invention, the view being similar to Fig. 3; and

Fig. 5 is a sectional view showing the arrangement of the inlet and outlet connections in the Fig. 4 embodiment of the invention.

The present invention comprises a magnetic drag pump which is preferably formed of a hollow member which defines a continuous passage between an inlet and an outlet. This passage is for the purpose of confining an electrically conducting liquid to be pumped, for example,

sodium orthe like, and preferably defines an arc of cur-, The pump includes movable vature around an axis. means for generating a magnetic field extending transversely through the passage comprising at least one pair of pole pieces positioned on opposite sides of the arcuate hollow member, and benig mounted for movement along opposite sides of the hollow member. In a preferred form of the invention the pair of pole pieces is spaced from, and is mounted for rotation around, an axis which is preferably coincident with the axis of curvature of the liquid-confining passage. During rotation, the magnetic flux between pole pieces of a pair defines a cylinder of revolution and the liquid-confining passage is positioned within this cylinder of revolution so that the liquid in the passage is subjected to the rotating magnetic field.

I have discovered that the electro-conductive characteristics of the passage-defining walls of such a pump in relation to their location with respect to the magnetic field constitute important factors in the efficiency of the pump. If these walls are of uniform conductive characteristics, the pump is either extremely ineflicient (if the wall conductivityis high) or virtually inoperative if States Patent part be obvious Q the walls have a high electric resistance. However, I- have found that by making those opposite portions of the passage walls which are interposed between the flux path and the liquid of high electrical resistance while providing high electrical conductivity in the wall portions at opposite sides of the flux path a great improvement in efficiency is obtained. This improvement is still further amplified if the highly conductive portions of the Walls are located substantially entirely outside the flux path.

In order to operate such a pump with a reasonable head, it is necessary to generate eddy currents of extremely large magnitude (on the order of several thousand arnperes) extending through the liquid in a plane transverse to the flux path. Due to the high magnitude of these eddy currents, it is necessary that a highly conductive return path be provided for the flow of these eddy currents outside of the liquid in a direction parallel to the flow of the liquid; On the other hand, by

providing walls of low conductivity interposed in the flux path between the pole face and the liquid, the generation of primary eddy currents in the low-conductivity walls (along with secondary eddy currents in theliquid which tend to oppose and interfere with the action of the primary eddy currents in the liquid) is effectively inhibited. The tendency. to generatethese detrimental eddy currents in the wall between the pole face and the liquid is very great due to the fact that the relative motion between the pole face and the wall is much greater than the relative motion between the pole face and the liquid being pumped. 4

Additionally, by locating the highly conductive wall portions substantially outside of the flux path, the generation of eddy currents lying entirely within these highly.

conductive portions is minimized and the pumping efficiency enhanced, because such currents represent wasted energy, giving rise to no pumping force but, on the contrary, generating forces counteracting the movement of the field and producing undesirable heating of the walls.

Accordingly, in a preferred embodiment of the inven-' tion, those opposite liquid-confining walls of the hollow member which are adjacent the magnetic pole pieces and. interposed between the liquid and the pole face are" formed of a material having a high electrical resistivity which acts to minimize eddy currents in these walls due to the moving magnetic field. Additionally, these walls are preferably as thin as is consistent with adequate rnechanical strength. The side Wall portionsqlbetween I these electrically resistant walls) provided for'returnof' induced currents are formed of, or comprise material of,

high electrical conductivity which is effective to form, with the liquid in the passage, a closed electric circuit favorableto' the flow of high amperage eddy currents in" i I v It is also preferred that these high-conductivity portions of the a plane transverse to the flux path of the field.

hollow member are not subjected, to any substantial extent, to the high intensity moving magnetic field, thereby avoiding the generation of eddy currents flowing entirely within these high-conductivity portions. these high-conductivity portions are preferably concentrically spaced from the cylinder of revolution defined by the pole faces during rotation thereof. It "is not essential that the highly conductive wails be formedenv tirely of conductive material so long as any portion of material of high electrical resistivity between the liquid and the highly conductive portion is perpenidcular to the eddy current path and is relatively thin so that the total efiective impedance of the eddy current path is low.

Accordingly,

Referring now to Figs. 1 through 3, there is illustrated a schematic representation of one type of pump embody: ing the present invention. In these figures, wherelilge numbers refer to like elements in the other figures, the

hollow member is generally indicated at 10, this member having an arcuate liquid-confining passage 12 therein.

The. hollow member. 10 isstationarily supported on a snitableframe 11 by means suchas' asupport schematically indicated at 13. The passage. 12 is provided with suitable} inlet: and outlet openings. (not. shown) for'the liquid :metaL. severalipairstfour being ShWn).Ofe1C- I tromagnetic polepieces 14 are mounted for :rotation with respect to the hollow member. 19 so that thezliquidwithin.

the. passage 12. is. subjected to. a; high density, moving magnetic field, .thisfield moving along the passage 12 in the direction desired forrnotion of the liquid. As shown particularly in Figs. 1 and 2, those walls 16 of. the member 10.which,lie paralleltothe planesof rotation of the polefaces, andbetweenthe pole faces, are formed of a rectangular liquid-confining passage, 12.

The .polepieces 14 are supported by pole members which,,with'. flanges .22' and shaft 24, ,made 1 of ferromagnetiematerials, complete the magnetic circuit betweenthe pairs.oflfpolepieces. A. pair ofelectromagnetic coils 26. are preferably providedfor generating a strongmag netic field in the magnetic circuit constituting the .mem: bets 24,22, 20. and. 14. The electromagnetic. field is preferably a, DC. field. so thatthereis' a constant high unidirectional. flux .density extending between pole pieces. 14;. preferably onthe order of eight to ten thousand gaussl The magneticelements, including thepolepieces and. coils 26, are. preferably supported on arotating. shaft 28, carried by. bearings mounted on frame: 11-.

This. shaft 28 may bedrivenby apulley. 32, connected:

to a suitable. motor (not shown).

. In. order to. obtain maximum flux density, the gapbe tween the pole pieces should be as small as possible.

I These highly conductive portions are indicatedat 18, anddefine, along with walls 16, the

field m? will be substantially equal to the transverse dimension l of the passage 12. It is equally important that the propulsive forces proportional to magnetic field density be uniform across the fluid channel. There-.

fore, it is essential that the transverse dimension fp of the pole face not be made too small. Otherwise, the transverse dimension m ofthe magnetic field will not coincide with the transversedimension fl of the passage 12, and poor hydraulic efliciency resulting from nonuniform propulsive forces across the liquid passage 12 will be obtained. Thus, the magnetic circuit should preferably be such that all the liquid in the passage is subjected to -a uniform moving magnetic'field, this field being preferably substantially as large as the cross section of the passage, but no larger.

Referring now more particularly to Fig. 3, there is shown (on a considerably enlarged scale) therelationship between the pole pieces 14, the liquid-confining passage-12,,the high-conductivity portions 18, and the liquid to be pumped; In Fig. 3 the liquid is to be pumped from leftltd right in the passage 12 (i.e.,.in a clock wise direction), The pole pieces14 (shown in dotted lines) accordingly move in this direction, the movement t of the pole pieces 14 and theliquid beingshown by However, the smaller=the gap, the less room for the liquidpassage 12. Accordingly, the passage is preferably elongated in. the radial direction transverse to themagnet-ic field to obtain. adequate cross. sectional area even with a relatively narrow gap between the. pole pieces.

Thus, in a preferred embodimentof the. invention (as. showninFig. 2), the radial'dimension l of the: liquid.

passage. 12, transverse. to the magnetic. field, is greater than the. thickness .t? of-thepassage ilalong .the dimension. parallel tothe magnetic lines of'force. The beneficialjeffect ofextending the transverse. dimension 1 of Y the liquid passagemust be balanced against the increased hydraulic. resistance. which. is obtained as the wetted perimeter offthe liquid passage increases. Accordingly, in. any particular case, it is necessary to compromise betweenthedesirability of 'having'a small gap between the .pole faces and the necessity of avoiding undue hydraulic frictional lossesin'the passage. Similarly, the, thick- .fti? of the'high resistivity wall 16'sh'ould be as small as possible, consistent with :the. mechanical requirements of,

this wall.'. The airgap d between a'pole' face and the adjacentwalll 16 should also be madeas small as pos sible, consistentwith the-Irequirements'of dynamic balformed of stainless *steel;

- solid arrows. As a pair ofpole pieces 14 moves to the right, they create two eddy currents in the conducting"v liquid. The induced currents flow in the liquid in a direction generally perependicular to the flow of the stream a and the magnetic field, and flow through the high-conductivity; portions 18 in, a path whichis generally paral::

lel to the passage 12.

'These'eddy currents generate electromagnetic fields of their own which tend to: follow the magnetic "field-be Thus, as the pole .pieces move, the induced electromagnetic fields: tend to movelwith the.

tween. the pole pieces.

pole pieces, thereby producing within the conductiveqfluid propulsive: forces moving. the liquid metal." Whenthe liquid does not move as fastas the pole pieces, the eddycurrents increase'a's a functionof'the difference between the speed of the'pole pieces'andthe speedof the liquid.

Thus,-",tl1'e greater. this dilference,;the" greater arethe eddy currents generated in thepumped' liquid. andthe greater are the. resultant electromagnetic (and consequentlypropulsive) .xforces .tending. to: move :the'; liquid:

Ina preferred method of manufacturing thelpump of Figsz; l through 3; the! liquid-"conductingpassage. 12 1s formed'from two :concentric recessed copper. discs 18, to the two recessed faces of which are brazedatwothm stainless steel discs 16'.

and outlet: openings; The pole pieces, and" the remain der' of-the magnetic circuit, are made o f aferromagnetic material such as iron and thecoil and magnetic circuit arezpreferably designedto give high flux densit es on the: order"of 8,000tolofiloOgauss. l

- Referring now to'Figs. 4 and 5, there is shownanother, embodiment of the-invention which is particularly adapt+ ed to the pumping of liquid metals at'relatively high tem-:

per'atures ou the i order of 800. C. In 1 this I embodiment the liquid-confining passa e 12-of the hollow member 1t? 1; is" defined by an arcuate flattenedtube 34,- preferably The high-conductivity por- 4 tion of the hollow member 19, which'is provided outside ancing-.of.. tlie. machine. As illustrated in Fig. 2,. the

transverse dimension "p of the pole face'should be less than thetransverse dimension 1 of the liquid-confining passage 12. so that the transverse dimension in of the expanding hi gli density' magnetic field will not penetrate appreciabl'y' into thehighwonductivity'portions 18; For

results; the transverse" dimension of themagn of the magnetic field but in the plane of 1 the liquid metal",

now; is; furnished; by stainless steel tubes 36*which are filled wim-copper 33: The 'composite hollowrnembeb it} (including elements 34, 36 and 38"thereof) is carried by a 'pluralityof' resilient supports 40' comprisingp1ns' 41' sliding in sle'evesi42'rrigidly"mounted on=frame 11.

These pins 41 are normally gheld [against axial movement by springs 44. This arrangementof'elements permitsexpension and-contraction of thehollbwihember 10, in the planethereofldue to compression or expansionjof spr ngs 44) with changes temperature of the hollow member. However, the support 40. holds.tlie member ltl rtgidly.

A circular passage is thus formed, this passage beingi provided. withsuitable inlet against any changes in a direction normal to the plane thereof. This construction accordingly permits operation over a wide range of temperatures while allowing the maintenance of close tolerances between the plane of rotation of the pole pieces 14 and the sides of the flattened tube 34.

In the manufacture of this embodiment of'the pump, the tubes 36 are welded to the outer and inner circumferences of the flattened tube 34, and are then heated in a hydrogen filled atmosphere to remove surface oxide and the like. While the composite structure is highly heated, molten copper is poured into the outer tubes 36 so as to completely fill these tubes with molten copper which, when solidified, is intimately bonded to the inner and outer circumferences of the flattened tube 34. The outer surfaces of the stainless steel tubes 34 and 36 are then prefereably gold-plated so as to provide a surface 37 (Fig. 4) having a low coefficient of heat radiation. The pump is also preferably provided with a radiation heat shield 46 (Fig. 4) positioned between the hollow member 10 and the electromagnetic coil 26 to prevent radiation damage to this coil at extremely high temperatures.

In the specification and drawings four pairs of pole pieces have been illustrated and described. This is one preferred embodiment of the invention. However, the invention should not be so limited. While four pairs of pole pieces have been illustrated, it is quite apparent that there can be many more pole pieces or even fewer. One pair of pole pieces will operate the pump, although such a construction creates difficult dynamic balancing problems and is apt to give a pulsating pumping effect.

While the invention has been particularly described in connection with the pumping of liquid metals, it is equally applicable to the pumping of other conducting liquids, such as molten salts, and slurries. Accordingly, the expression liquid is intended to include slurries, as well.

In the preferred embodiment of the invention illustrated in the drawings, the magnetizing force is supplied by electric coils 26. These coils are preferably energized with a DC. current which can be supplied through suitable commutators (not shown). Equally, the rotating shaft 28 can carry a D.C. generator so that no electrical leads need be supplied to the pump. Alternatively, the magnetic field may be supplied, by permanent magnets formed of a strongly magnetic material, such as Alnico.

Since certain changes may be made in the above process without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description, or shown in the accompanying drawings, shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In a magnetic drag pump for electrically conducting liquid which includes a passage for the liquid, and magnetic means for generating a magnetic field extending transversely through said passage and movable longitudinally thereof to exert pumping action on the liquid therein, a hollow member forming said passage and having liquid-confining walls completely surrounding the same, said walls having portions thereof at opposite sides of the flux path of said field comprising material of high electric conductivity effective to form with said liquid an electric circuit favorable to the fiow of highamperage eddy currents in a plane transverse to said flux, said portions being disposed substantially entirely outside of said flux path to minimize production of eddy currents flowing entirely within said portions, saidhollow member comprising a curved flattened tube arranged in a plane substantially normal to said flux path, said tube being formed of a material of high electrical resistivity and having the material of high conductivityintimately secured to the inner and outer circumferences thereof, and means supporting said tubeat a plurality of points around the outer circumference thereof to permit expansion and contraction in the plane thereof while preventing movement of said tube in a direction transverse to the plane thereof.

2. In a magnetic drag pump for electrically conducting liquid which includes a passage for the liquid, and magnetic means for generating a magnetic field extending transversely through said passage and movable longitudinally thereofto exert pumping action on the liquid therein, a hollow member forming said passage and having liquid-confining walls completely surrounding the same,

said walls having portions thereof at opposite sides of the flux path of said field comprising material of high electric conductivity effective to form with said liquid an electric circuit favorable to the flow of high-amperage eddy currents in a plane transverse to said flux, said portions being disposed substantially entirely outside of said flux path to minimize production of eddy currents flowing entirely within said portions, the outer surfaces of said hollow member including a coating having a low coefiicient of radiant heat transfer, and a radiant-heat shield provided between said member and an electromagnetic coil serving as a portion of the means for generating the magnetic field.

References Cited in thefile of this patent UNITED STATES PATENTS 1,298,664 Chubb Apr. 1, 1919 2,099,593 Bender et a1. Nov. 16, 1937 2,386,369 Thompson Oct. 9, 1945 2,651,258 Pierce Sept. 8, 1953 2,652,778 Crever Sept. 22, 1953 2,658,452 Donelian Nov. 10, 1953 2,686,474 Pulley Aug. 17, 1954 FOREIGN PATENTS 126,947 Great'Britain Dec. 24, 1919 OTHER REFERENCES Publication: Argonne National Laboratory report No. 4273, dated April 5, 1949, entitled Reactor Engineering Division Report for the Period Dec. 1, 1948, through Feb. 28, 1949, W. H. Zinn, Director.

Publication: Argonne National Laboratory report No. 4317, also known as AECD-343l, dated July 15, 1949, entitled Electromagnetic Pump for Liquid Metals, by A. H. Barnes, F. A. Smith and G. K. Whitham, pages 1-8, 11 and 12.

Publication: Liquid Metals Handbook, dated June 1, 1950, pages 156-161. 

